Sound absorbing laminates

Abstract

A process for forming sound absorbing laminates and the resulting laminate which comprises at least one layer of nonwoven fibers bonded to a substrate by a thermoplastic adhesive. The laminate is formed by placing a layer of bonded nonwoven fibers into contact with a substrate and bonding the layer of nonwoven fibers to the substrate. The improvement comprises: utilizing at least one layer of nonwoven fibers coated with an aqueous emulsion of a vinyl acetate-ethylene (VAE) adhesive and then dried. The VAE adhesive is prepared by aqueous emulsion polymerization, contains crystalline ethylene segments and has: (a) a crystalline melting point (T m ) ranging from 35 to 110° C., preferably 50 to 100° C.; measured at a heat rate of 20° C./minute; and, (b) a tensile storage modulus of at least 1×10 4 dynes/cm 2 at 115° C. measured at a test frequency of 6.28 rad/sec.

1 . In a sound absorbing laminate having at least one layer of nonwoven fibers bonded to a sound absorbing substrate by a thermoplastic adhesive, said laminate formed by placing a layer of nonwoven fibers onto said sound absorbing substrate and applying sufficient heat to activate the thermoplastic adhesive and bond the layer of nonwoven fibers to said sound absorbing substrate, the improvement which comprises: 
 utilizing in said sound absorbing laminate at least one layer of a web of nonwoven fibers coated first with an aqueous emulsion of a vinyl acetate-ethylene adhesive polymer and then the water removed therefrom, said vinyl acetate-ethylene adhesive polymer comprised of crystalline ethylene segments prepared by aqueous emulsion polymerizing ethylene and vinyl acetate in the presence of a stabilizing system, said vinyl acetate-ethylene adhesive polymer having:    (a) a crystalline melting point ranging from 35 to 110° C. measured at a heat rate of 20° C. per minute; and,    (b) a tensile storage modulus of at least 1×10 4  dynes/cm 2  at a temperature of 115° C. and measured at 6.28 rad/sec.    
   
   
       2 . The sound absorbing laminate of  claim 1  wherein the vinyl acetate-ethylene adhesive polymer is comprised of from 25 to 80% by weight of polymerized units of vinyl acetate and from about 20 to 75% by weight of polymerized units of ethylene, based upon the total weight of the polymer.  
   
   
       3 . The sound absorbing laminate of  claim 1  wherein the vinyl acetate-ethylene adhesive polymer is comprised of from 35 to 75% by weight of polymerized units of vinyl acetate and from about 25 to 65% by weight of polymerized units of ethylene, based upon the total weight of the polymer.  
   
   
       4 . The sound absorbing laminate of  claim 2  wherein polymerized carboxylic acid units are present in said vinyl acetate-ethylene adhesive polymer in an amount from about 0.2 to about 10% by weight of said polymer.  
   
   
       5 . The sound absorbing laminate of  claim 4  wherein said vinyl acetate-ethylene adhesive polymer has a tensile storage modulus of at least 2×10 4  dynes/cm 2  at 115° C. and measured at 6.28 rad/sec.  
   
   
       6 . The sound absorbing laminate of  claim 5  wherein the vinyl acetate-ethylene adhesive polymer is comprised of polymerized units of ethylene, vinyl acetate, and acrylic acid.  
   
   
       7 . The sound absorbing laminate of  claim 5  wherein the crystalline heat of fusion of said vinyl acetate-ethylene adhesive polymer is from about 5 to 100 joules per gram measured at a heat rate of 20° C. per minute.  
   
   
       8 . The sound absorbing laminate of  claim 7  wherein the glass transition temperature of said vinyl acetate-ethylene adhesive polymer is from +25° C. to about −35° C. as measured at a heat rate of 20° C. per minute.  
   
   
       9 . The sound absorbing laminate of  claim 8  wherein crystalline thermal melting point of said vinyl acetate-ethylene adhesive polymer ranges from 50 to 90° C. as measured at a heat rate of 20° C. per minute.  
   
   
       10 . In a process for forming a sound absorbing laminate wherein a web of nonwoven fibers is bonded to a sound absorbing substrate by the application of pressure and heat, the improvement which comprises: 
 (a) coating said web of nonwoven fibers with an aqueous polymer emulsion, wherein the polymer of the aqueous polymer emulsion contains emulsion polymerized units of vinyl acetate and ethylene, said polymer having: 
 (i) a crystalline melting point ranging from 35 to 110° C. measured at a heat rate of 20° C. per minute; and,  
 (ii) a tensile storage modulus of at least 1×10 4  dynes/cm 2  at a temperature of 115° C. as measured at 6.28 rad/sec;  
   (b) drying the coated nonwoven web of fibers thereby forming a coated and dried nonwoven web;    (c) placing the coated and dried nonwoven web in contact with a sound absorbing substrate thereby forming a laminate; and,    (d) placing the laminate in a mold and applying sufficient pressure and temperature to bond the coated and dried web of nonwoven fibers to said sound absorbing substrate.    
   
   
       11 . The process of  claim 10  wherein the sound absorbing substrate is selected from the group consisting of polystyrene, polyethylene, and polyurethane foam core.  
   
   
       12 . The process of  claim 11  wherein the coated and dried nonwoven web of fibers formed in step (b) is wound into a roll thereby forming a rolled nonwoven web of fibers or the coated and dried nonwoven web of fibers is cut into sheets and put into stacks; subsequently unwinding the rolled nonwoven web of fibers or separating the stacked sheets, and placing the coated side of the coated and dried nonwoven web of fibers into contact with a sound absorbing substrate thereby forming a laminate.  
   
   
       13 . The process of  claim 12  wherein the fibers of said coated and dried nonwoven web of fibers comprise synthetic polymers.  
   
   
       14 . The process of  claim 12  wherein the fibers in said coated and dried nonwoven web fibers are selected from the group consisting of polypropylene, polyamide, polyethylene, and polyester.  
   
   
       15 . The process of  claim 14  wherein polymerized units of vinyl acetate are present in the vinyl acetate-ethylene polymer in an amount from 15 to 90% by weight, polymerized units of ethylene are present in an amount from 10 to 85% by weight, and polymerized units of acrylic acid are present in an amount from 0.5 to 5% by weight of the polymer.  
   
   
       16 . The process of  claim 15  wherein the crystalline heat of fusion in said vinyl acetate-ethylene adhesive polymer ranges from 15 to 70 joules per gram as measured at a heat rate of 20° C. per minute.  
   
   
       17 . The process of  claim 12  wherein the coated side of one sheet or roll of coated and dried nonwoven web of fibers is placed in contact with one side of said sound absorbing substrate and the coated side of another sheet or roll of coated and dried nonwoven web is placed in contact with the opposite side of said sound absorbing substrate.